At the time of this proposal, this work was not NIH funded, although there are two proposals submitted, and some Institutional Faculty Awards are in effect): The investigators are using two characterized proteins in the plasma membrane of guinea pig sperm to investigate diffusion within the membrane. These proteins redistribute during the capacitation and aerosomal reaction. The investigators have published on this redistribution ten years ago. The virtual cell project may provide resources to answer questions concerning whether extracellular elements restrict diffusion of one of the proteins. 6